This invention relates to a variety of improvements applicable to a composite unit of an optical semiconductor device and a supporting substrate and to a variety of improvements applicable to a method for mounting an optical semiconductor device on a supporting substrate.
An optical fiber may be employed to transmit an optical signal emitted by a light emitting diode or a laser diode and/or an optical signal received by a photo diode. Accordingly, connection of an optical fiber and an optical semiconductor device, e.g. a light emitting diode a laser diode or a photo diode, is an important parameter in the technical field of optical signal transmission. In this sense, development of a device employable for coupling or uncoupling an optical fiber and an optical semiconductor device is a long standing subject to enhance the optical signal transmission technology and to cause the optical signal transmission technology to prevail in society.
The requirements for such a device include the function of connecting an optical fiber and an optical semiconductor device in a manner such that the optical axes of both are accurately aligned each other, and the function of allowimg connection and disconnection of an optical fiber and an optical semiconductor device without requiring any skill.
An example of such a device was disclosed in a technical document entitled "Development of a surface mounting optical module" written by Kurata et al. and presented at a convention of the Electronics Society held by Institute of Electronics, Information and Communication Engineers in 1995.
Referring to the drawings, a composite unit of an optical semiconductor device and a supporting substrate disclosed in the document will be described below.
Referring to FIG. 1, a supporting substrate (1) made of an Si plate of which the top surface is covered by an SiO.sub.2 film is provided with a pair of marks (1a) as positioning marks, an electrode pattern (1b) produced thereon, and a V-groove (1c) is provided to receive an optical fiber (not shown). A square shown with a broken line shows the location at which an optical semiconductor device which will be described later is scheduled to be placed.
Referring to FIG. 2, an optical semiconductor device (2) having an anode (not shown) produced on the top surface thereof and a cathode (not shown) produced on another surface thereof is provided with a pair of marks (2a) produced on the rear surface thereof as positioning marks at locations corresponding to the foregoing positioning marks (1a) produced on the supporting substrate (1), and an electrode pattern (2b) is produced on the surface of the cathode.
Referring to FIG. 3, the optical semiconductor device (2) is placed on the supporting substrate (1), and Infrared rays are radiated toward the rear surface of the supporting substrate (1) to observe the image of the two pairs of marks (1a) and (2a) on a screen (4) located above the optical semiconductor device (2). The optical semiconductor device (2) is slightly slid along the top surface of the supporting substrate (1) to align the images of the two pairs of marks (1a) and (2a). In this manner, the location of the optical semiconductor device (2) is adjusted on the supporting substrate (1) with an accuracy less than 1 .mu.m, Thereafter, the optical semiconductor device (2) is soldered to the supporting substrate (1) The foregoing composite unit of an optical semiconductor device and a supporting substrate and the method for mounting an optical semiconductor device on a supporting substrate are, however, involved with the drawbacks tabulated below.
1. The process for mounting an optical semiconductor device on a supporting substrate is complicated and requires a sizable amount of time and labor. Particularly, the process for adjusting two marks is troublesome.
2. The accuracy in adjustment of the two pairs of the positioning marks is unsatisfactory, due to irregular reflection of infrared rays caused by roughness of the surfaces of the optical semiconductor device (2) and of the supporting substrate (1).
3. The accuracy in adjustment of the height of the active layer or the optical axis of an optical semiconductor device and the height of the center of the core of an optical fiber is unsatisfactory, because the height of the active layer or the optical axis of an optical semiconductor device inevitably varies depending on the thickness of a layer of solder which fixes the optical semiconductor device and the supporting substrate.